Method and apparatus for detecting backside contamination during fabrication of a semiconductor wafer

ABSTRACT

A method of detecting contamination on a backside of a semiconductor wafer includes the steps of positioning the backside of the wafer in contact with a detection surface of a contaminant sensor, and detecting deformation of the detection surface of the contaminant sensor. The contaminant sensor may be incorporated into a fabrication device such as a wafer handling device, or can be utilized in the construction of a stand-alone device. An apparatus for detecting contamination on the backside of a semiconductor wafer is also disclosed.

[0001] This application is a divisional application of copending U.S.patent application Ser. No. 10/138,742 which was filed on May 3, 2002and is incorporated herein by reference.

TECHNICAL FIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to semiconductor waferfabrication, and more particularly to a method and apparatus fordetecting backside contamination during fabrication of a semiconductorwafer.

BACKGROUND OF THE DISCLOSURE

[0003] Semiconductor integrated circuits are typically fabricated by alayering process in which several layers of material are fabricated on asurface of a wafer. Contamination on the backside of the wafer (i.e.,the side of the wafer opposite to the surface being layered) is asignificant contributor to problems during fabrication. In particular,contamination on the backside of the wafer may cause fabrication defectsat a number of different processing steps. For example, the presence ofbackside contamination may cause over etching or under etching duringthe chemical etching process or during the chemical-mechanical polishingprocess (CMP). Moreover, the presence of backside contamination may alsocause imaging-related defects during process steps such asphotolithography, wafer inspection, or during rapid thermal annealing(RTA). Backside contamination may also be the cause of poor surfacecontact with the backside of the wafer during processes which utilize RFor heat transfer to the backside of the wafer such as during the etchingprocess or RTA.

[0004] Large contamination particles may even be undesirably transferredto the front side of the wafer thereby potentially causing scratching ofthe front side of the wafer or the “micromasking” of a portion of thefront side of the wafer. In some extreme cases, the presence of backsidecontamination may even cause wafers to be broken due to stress or lossof vacuum pressure during wafer handling.

SUMMARY OF THE DISCLOSURE

[0005] In accordance with one aspect of the present disclosure, there isprovided a method of fabricating a semiconductor wafer. The methodincludes the steps of positioning the wafer in a wafer handling device,and detecting presence of a contaminant on a backside of the wafer whilethe wafer is positioned in the wafer handling device.

[0006] In accordance with another aspect of the present disclosure,there is provided an apparatus for fabricating a semiconductor wafer.The apparatus includes a wafer handling device. A contaminant sensor issecured to the wafer handling device. The contaminant sensor isconfigured to detect presence of a contaminant on a backside of thewafer when the wafer is positioned in the wafer handling device.

[0007] In accordance with a further aspect of the present disclosure,there is provided a method of detecting contamination on a backside of asemiconductor wafer. The method includes the steps of positioning thebackside of the wafer in contact with a detection surface of acontaminant sensor, and detecting deformation of the detection surfaceof the contaminant sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIGS. 1-6 are cross sectional views of a semiconductor waferduring various steps of a wafer fabrication process;

[0009]FIG. 7 is a cross sectional view of contaminant sensor beingutilized to detect presence of a contaminant on the backside of asemiconductor wafer;

[0010]FIG. 8 is an enlarged view similar to FIG. 7, but showing aspecific exemplary embodiment of a contaminant sensor; and

[0011]FIG. 9 is a diagrammatic cross sectional view which shows acontaminant sensor integrated into a wafer handling device.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0012] While the disclosure is susceptible to various modifications andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and will herein be described in detail. Itshould be understood, however, that there is no intent to limit thedisclosure to the particular forms disclosed, but on the contrary, thedisclosure is to cover all modifications, equivalents, and alternativesfalling within the spirit and scope of the disclosure as defined by theappended claims.

[0013] Referring now to FIGS. 1-6, there is shown a semiconductor wafer10 during various steps of a fabrication process. The semiconductorwafer 10, as shown in FIGS. 1 and 2, includes a semiconductor substrate12, such as silicon. A first insulating layer 14 and a first metal layer16 are deposited or otherwise disposed on the semiconductor substrate12. In particular, the fabrication process deposits the first insulatinglayer 14 on the semiconductor substrate 12 such that a contact hole 18is formed in the first insulating layer 14 at a location above atransistor portion of the semiconductor substrate 12. Moreover, thefabrication process patterns the first metal layer 16 over the firstinsulating layer 14 and the contact hole 18. As a result, the firstmetal layer 16 fills the contact hole 18 forming an electrical contactwith the transistor portion of the semiconductor substrate 12. Moreover,the filling of the contact hole 18 forms a pit 20 in the portion of thefirst metal layer 16 disposed above the contact hole 18.

[0014] As shown in FIG. 3, a second insulating layer 22 is deposited onthe outer surface of the first insulating layer 14 and the first metallayer 16. The second insulating layer 22 has an uneven surfacetopography as a result of the varying topography associated with thefirst insulating layer 14 and a first metal layer 16. A polishingprocess such as a chemical-mechanical polishing (CMP) process may beutilized to polish the second insulating layer 22 down to a desiredlevel 24 thereby planarizing the surface of the second insulating layer22 (see FIG. 1D).

[0015] As alluded to above, once the semiconductor wafer 10 has beenpolished such that a planar surface is created, additional layers may bedeposited or otherwise fabricated thereon. For example, as shown inFIGS. 5 and 6, a via hole 26 may be patterned via a lithography processand thereafter formed through the second insulating layer 22 via anetching process. Thereafter, a second metal layer 28 may be deposited onthe second insulating layer 22. It should be appreciated that numerousadditional layers may be deposited on the semiconductor wafer 10 in themanner previously described.

[0016] During such a wafer fabrication process, along with waferfabrication processes having numerous additional or fewer process steps,contamination can accumulate on a backside 30 of the semiconductor wafer10. Such contamination may take on many forms such as particles, debris,or the like that accumulate on the backside 30 of the semiconductor 10as a result of the numerous process and handling steps.

[0017] As shown in FIG. 7, a contaminant sensor 32 may be utilized todetect presence of a contaminant 34 on the backside 30 of thesemiconductor wafer 10. The contaminant sensor 32 may be any type ofsensing device for sensing presence of contaminants of the sizetypically associated with wafer fabrication. In illustrativeembodiments, the contaminant sensor 32 is embodied as a pressure sensingfilm which senses pressure changes (e.g., pressure increases) as aresult of deflection or deformation of an outer surface thereof.Specifically, the pressure sensing film used in the construction of thecontaminant sensor 32 may be configured to sense two distinct states. Inthe case of when the backside 30 of the wafer 10 is devoid ofcontamination 34, an even compression is present across the film.However, when an outer detection surface 36 of the film deflects orotherwise deforms as a result of contamination 34 being trapped betweenthe contaminant sensor 32 and the backside 30 of the semiconductor wafer10, a local pressure will be created in the pressure sensing film.Presence of this local pressure triggers the sensor 32.

[0018] In such a way, the sensor 32 senses deflection or deformation ofthe detection surface 36 and generates an output signal indicativethereof. The output signal generated by the contaminant sensor 32 may beutilized by one or more control systems associated with the waferfabrication process. For instance, the control system associated with awafer handling device may utilize the output signal from the contaminantsensor 32 to determine whether the wafer 10 is to be advanced to, forexample, (i) a subsequent processing step in the case of when the waferis devoid of backside contamination, or (ii) an offline rework stationin the case of when contamination is detected on the backside 30 of thewafer 10.

[0019] Similarly, the wafer loader associated with a piece offabrication equipment may be equipped with a contamination sensor 32 tomonitor the output signals therefrom to determine if backsidecontamination is present on the wafer prior to commencement of theprocess being performed by the equipment. Conversely, the wafer unloaderassociated with a piece of fabrication equipment may be equipped with acontamination sensor 32 to monitor the output signals therefrom todetermine if backside contamination was introduced onto the wafer duringthe process being performed by the equipment.

[0020] As described herein, the contaminant sensor 32 may embodied as anumber of different types of pressure sensitive films. For example, thecontaminant sensor 32 may be embodied as a thin pressure sensing filmthat includes one or more micro strain gauges. Such a thin film may beconfigured to sense changes in pressure across the entire area of thefilm. Alternatively, the film may be configured in a grid-like patternthereby producing a number of smaller, local sensing areas. In thismanner, several distinct areas of the backside 30 of the wafer 10 may bemonitored to produce data indicative of the density, size, and locationof the backside contaminants.

[0021] The thin pressure sensing film may also be configured as a liquidcrystal film. In such a configuration, a liquid crystal media isinterposed between a light source and a light receptor. Deformation ordeflection of the liquid crystal media distorts the transmission oflight generated by the light source through the media, with suchdistortion being detected by the light detector. This phenomena isexemplified by pressing or otherwise applying pressure to the outersurface of a liquid crystal display screen such as the display screentypically associated with a laptop computer.

[0022] The pressure sensing film may also be configured as themulti-layered film assembly 46 shown in FIG. 8. In particular, thecontaminant sensor 32 may be constructed to include a pair of conductivefilms 40, 42, with a dielectric film 44 therebetween. In such aconfiguration, the sensing surface 36 is defined in the conductive film40. A “base” capacitance of the film assembly 46 may be determined basedon the stored charge in the “gap” between the conductive films 40, 42created by the dielectric film 44. When contamination 34 is present onthe backside 30 of the wafer 10, the conductive film 40 is deflected,deformed, or otherwise urged in the general direction of the conductivefilm 42 thereby changing the width of the gap between the two films 40,44. This change in width of the gap changes the capacitance of theassembly. Such a change is capacitance is detected by the contaminationsensor 32 thereby causing the sensor 32 to generate an output signal foruse by a system controller in the manner described above.

[0023] As alluded to above, the contaminant sensors of the presentdisclosure may be utilized in a number of different manners within thewafer fabrication process. For example, as shown in FIG. 9, thecontaminant sensor 32 may be incorporated into a wafer handling device50 such as a processing chuck, an alignment apparatus, a wafer handlersuch as a load fork or the like. In such a case, as shown in FIG. 9, thesensor 32 is interposed between a support surface 52 of the waferhandling device 50 and the backside 30 of the wafer 10. Alternatively,in lieu of integration into an existing apparatus, the contaminantsensor 32 may be incorporated into a “stand alone” device which isoperated for the purpose of detecting backside contamination.

[0024] While the concepts of the present disclosure has been illustratedand described in detail in the drawings and foregoing description, suchillustration and description is to be considered as exemplary and notrestrictive in character, it being understood that only exemplaryembodiments have been shown and described and that all changes andmodifications that come within the spirit of the concepts of the presentdisclosure are desired to be protected.

[0025] There are a plurality of advantages of the concepts of thepresent disclosure arising from the various features of the apparatusand methods described herein. It will be noted that alternativeembodiments of the apparatus and methods of the present disclosure maynot include all of the features described yet still benefit from atleast some of the advantages of such features. Those of ordinary skillin the art may readily devise their own implementations of the apparatusand methods of the present disclosure that incorporate one or more ofthe features of the present disclosure and fall within the spirit andscope of the invention defined by the appended claims.

1. An apparatus for fabricating a semiconductor wafer, comprising: awafer handling device, and a contaminant sensor secured to the waferhandling device, the contaminant sensor being configured to detectpresence of a contaminant on a backside of the wafer when the wafer ispositioned in the wafer handling device.
 2. The apparatus of claim 1,wherein the contaminant sensor comprises a deformable detection surfaceconfigured to contact the backside of the wafer when the wafer ispositioned in the wafer handling device.
 3. The apparatus of claim 1,wherein: the contaminant sensor is configured to output (i) a firstcontrol signal indicative of a first capacitance value when the backsideof the wafer is devoid of contaminant particles, and (ii) produce asecond control signal indicative of a second capacitance value when acontaminant particle is present on the backside of the wafer, and thefirst control signal is different from the second control signal.
 4. Theapparatus of claim 1, wherein the contaminant sensor comprises a firstconductive film, a second conductive film, and a dielectric filmpositioned between the first conductive film and the second conductivefilm.
 5. The apparatus of claim 4, wherein the first conductive film isconfigured to contact the backside of the wafer when the wafer ispositioned in the wafer handling device.
 6. The apparatus of claim 1,wherein the contaminant sensor comprises a pressure sensing film.
 7. Theapparatus of claim 1, wherein the contaminant sensor comprises a liquidcrystal film.